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NEET Sample Paper NEET Sample Test Paper-42

  • question_answer
    Half lives of two radioactive substances A and B are respectively 20(min) and 40(min). Initially the samples of A and B have equal number of nuclei. After 80min, the ratio of remaining number of A and B nuclei is:

    A) 1:16                 

    B) 4:1  

    C) 1: 4                  

    D) 1:1

    Correct Answer: C

    Solution :

    \[{{\operatorname{t}}_{A}}=20\,\,min\]                     \[{{\operatorname{t}}_{B}}=40\,\,min\] \[{{\operatorname{n}}_{A}}=\frac{T}{{{t}_{A}}}=\frac{80}{20}=4\,\,\,\,\,\,\,\,\,\,\,{{\operatorname{n}}_{\operatorname{B}}}=\frac{80}{40}=2\] \[\therefore {{N}_{A}}={{N}_{B}}(given)\] \[{{N}_{A}}={{N}_{\operatorname{o}}}{{\left( \frac{1}{2} \right)}^{4}}\,{{N}_{B}}=N{{\left( \frac{1}{2} \right)}^{2}}\] \[\frac{{{N}_{A}}}{{{N}_{\operatorname{B}}}}=\frac{1}{4}\]


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